A key factor in achieving accurate delivery of radiation therapy is patient positioning. It is important that patient positioning can be carefully controlled to accurately locate the target volume to be irradiated and avoid irradiation of surrounding healthy tissue. Existing patient support systems allow for movement of the patient in all six degrees of freedom. For example, the applicant's Precise™ treatment table allows for vertical, horizontal, longitudinal and lateral table movement and both column and isocentric rotation.
In addition to accurate patient positioning it is important to allow ease of access to the treatment table/couch for the patient. Patient support systems used with LINACs need to be positioned at a suitably low height (less than 600 mm) to enable patients to easily mount and dismount the treatment couch. It is also important that the PSS is moveable to a height in the region of 1700 mm above floor level to provide for a full range of treatment with unrestricted access to a wide range of LINAC positions. For example, it may be necessary to allow access beneath the couch and treatment at extended distances.
Existing PSS devices have achieved the required range of movement by providing a compact support system in combination with a long reaching lifting mechanism. Such a device is disclosed in the applicant's earlier U.S. Pat. No. 6,502,261 (the content of which is incorporated herein by reference in its entirety). It is also known for the PSS device to be supported in a cavity or well in the floor of the treatment room. For example, a load bearing element in a well of the treatment room floor is used to mount a lifting column, which adjusts the height of a treatment couch.
It is also common for the LINAC and PSS to be used in addition to a further patient positioning system. For example, the applicant's HexaPOD™ robotic patient positioning platform, which improves the accuracy of patent positioning by highlighting and correcting for any positional discrepancies. The use of an additional patient positioning system increases the minimum height at which the patient can be positioned. This can make it more difficult for a patient to mount and dismount the treatment couch.